Voltage regulated transistorized ignition system for an automobile turbine engine

ABSTRACT

An ignition system for a gas turbine engine that includes a current regulated transistorized oscillator in combination with a transformer and a spark plug in the secondary of the transformer to produce sparks to ignite fuel in the turbine.

United States Patent [191 Thakore 11 3,725,732 [451 Apr. 3, 1973 [54] VOLTAGE REGULATED TRANSISTORIZED IGNITION SYSTEM FOR AN AUTOMOBILE TURBINE ENGINE Inventor:

Kaushik H. Thakore, Sidney, N.Y.

The Bendix Corporation, Southfield, Mich.

F e bfzs, 19 72 Assignee:

E i led:

Appl. No.:

US. Cl. ..315/209 T, 123/148 B, 123/148 E, 307/275, 331/112 Int. Cl ..H05b 37/02, F02p 1/00 Field of Search ..l23/l48 B, 148 E; 307/275; 315/209 R, 209 T; 331/112 [56] References Cited UNITED STATES PATENTS 3,535,652 l0/l970 Minks ..315/209 X 3,431,901 3/1969 Rogers ..l23/l48 E Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl AttorneyRaymond J. Eifler et a1.

[5 7] ABSTRACT An ignition system for a gas turbine engine that includes a current regulated transistorized oscillator in combination with a transformer and a spark plug in 'the secondary of the transformer to produce sparks to ignite fuel in the turbine.

6 Claims, 2 Drawing Figures PATENTEDAPRS 1915 FIGURE 2 IGNITION CIRCUIT SPARK GAP I TURBINE ENGINE -22 FIGURE l VOLTAGE REGULATED TRANSISTORIZED IGNITION SYSTEM FOR AN AUTOMOBILE TURBINE ENGINE BACKGROUND OF THE INVENTION This invention relates to an electrical spark generating apparatus for gas turbine engines and the like.

Much difficulty has been experienced in providing a simple ignition system of small size, weight and with a minimum of components which will function satisfactorily to ignite so-called jet and gas turbine engines under all operating conditions. One example of a previous ignition system for a turbine engine is disclosed in U.S. Pat. No. 2,651,005 entitled Electrical Apparatus, to T. Tognola, issued Sept. 1, 1953. However, this type of device utilizes a vibrator to create the oscillations that cause an electrical discharge across a spark gap to ignite fuel in a turbine engine. The disadvantages of such a system are (l) the short mechanical life of a vibrator, (2) the short life of a battery used to drive the vibrator because the vibrator uses so much power, and (3) the cost of the entire circuit. Further, existing ignition systems for automobile turbine engines are bulky and expensive due to the fact that the wide range of operational voltages (4-10 volts d-c starting and -15 volts d-c running) requires components having wattage ratings sufficient to deal with the higher power associated with the system in the running mode.

SUMMARY OF THE INVENTION This invention provides a current regulated transistorized ignition system for an automobile gas turbine engine that utilizes less power than similar unregulated systems.

The ignition system is characterized by a current regulated oscillator circuit that produces a constant open circuit output voltage (22 volts) from an automobile battery over a wide range of input voltages (4-15 volts). The corresponding increase in power level normally associated with an increase in input voltage is also minimized.

In one embodiment of the invention the ignition system for an automobile gas turbine engine comprises: a battery for supplying a d-c voltage; a transformer having a primary winding and a secondary winding, with the secondary winding connected across a spark plug for igniting fuel in the engine; and a transistorized current regulated oscillator circuit that is connected to the battery and the primary winding of the transformer to periodically interrupt current from the battery to the primary winding whereby the oscillating current causes periodic electrical discharges across the spark plug to ignite the fuel in the turbine engine. The circuit described provides high energy output pulses at the spark discharge device over a wide range of input voltages available from an automobile battery. The circuit is further capable of operating under short or open circuit conditions at the secondary winding of the step-up transformer.

Accordingly, it is an object of this invention to provide a battery-powered current regulated transistorized ignition system for an automobile gas turbine engine.

It is another object of this invention to provide a transistorized ignition system for a gas turbine engine that requires only a spark gap discharge device in the secondary winding circuit of a step-up transformer.

It is still another object of this invention to provide a current regulated transistorized ignition system for a gas turbine engine that has a minimum amount of components.

It is still another object of this invention to provide a relatively inexpensive ignition system for a gas turbine engine that minimizes an increase in power input with a corresponding increase in voltage input.

A still further object of this invention is to provide a novel simplified ignition or spark producing system which is useful for igniting automobile gas turbine engines.

Another object of this invention is to provide an electrical apparatus for creating electrical sparks or arcs that are adapted for igniting combustible materials.

Yet another object of this invention is to provide a transistorized ignition system for a gas turbine engine that is capable of operating under open circuit and short circuit conditions in the secondary circuit of the step-up transformer without damage to the remaining components of the ignition circuit.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an ignition system for an automobile turbine engine.

FIG. 2 is a schematic diagram of a battery-powered transistorized ignition circuit that accomplishes the objects of this invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to FIG. 1, there is shown a block diagram of an ignition system for an automobile turbine engine which includes an ignition circuit 1 and a turbine engine 2 that includes a spark gap device 40 therein for igniting the fuel fed to the engine.

FIG. 2 is a schematic diagram of a preferred embodiment of the ignition circuit 1 shown in FIG. 1. The source of electrical energy for the circuit is a battery 3 which is an ordinary automobile battery or a d-c power supply having a voltage between 4 and 15 volts. The switch 5 is operable to connect and disconnect the battery to the circuit and is preferably a part of or associated with the ignition switch of an automobile. The spark gap discharge device 40 is a spark plug or the like which receives energy generated by the transistorized circuit and transformer 30. This causes a plurality of electrical discharges across spark gap 40 which occur at the same frequency rate as the current oscillations in the primary portion of the transformer 30.

The first portion of the oscillator circuit includes a resistor 11 in series with the emitter of transistor 10 which has its collector in series with resistor 12 and its base in series with resistors 15, 16 and diode 25. A diode 25 is connected to the junction of resistors 15, 16 andthe collector of transistor 20. When transistor 20 is non-conductive (OFF), diode 25 is reverse biased OFF and capacitor 9 charges through diode 23 and resistor 21. Zener diode 7, connected across the base-emitter junction of transistor 10, has a breakdown potential so that zener diode 7 will conduct in the reverse direction when the battery voltage exceeds a predetermined potential thereby causing transistor to conduct a substantially constant emitter-collector current in the steady state. The collector of transistor 10 is connected to the base of transistor 20 through lead 21 to provide a base current (drive) to transistor 20 when transistor 10 is conducting.

The second portion of the oscillator circuit includes blocking diode 13 connected in series with the collector of transistor 14 which has its emitter connected in series to series connected resistors 15, 16. The base of transistor 14 is connected to the components that direct the current from the primary 31 to capacitor 9 and the base of transistor 14. These components include resistors 21 and 22 in series with the base of transistor 14 and blocking diode 23 in parallel with resistor 22. This network allows capacitor 9 to charge when the voltage across the primary winding 31 of transformer 30 reverses as a result of transistor 20 turning OFF. When capacitor 9 is charged, a base current is supplied to transistor 14 turning transistor 14 ON. When transistor 14 is ON, the forward bias applied to transistor 10 is removed and transistor 10 is turned OFF.

The resistor 11 and zener diode 7 which are connected in the configuration shown form a constant current regulator. This provides a constant current output at the collector of transistor 10 regardless of increasing input voltages, thereby providing a constant base current drive through lead 21 to transistor 20. Hence the base drive of transistor 20 is fairly constant over the entire input voltage range. Since the collector current of transistor 10 is relatively constant, the ON time of the transistor 20 will decrease as the input voltage increases. Since the ON time of transistor 20 decreases as the input voltage increases, the input average current will also decrease if the OFF time of the transistor 20 is constant. In this system the OFF time of transistor 20 is a function of the ratio of the inductance of the secondary winding 32 of the transformer 30 to the resistance of the secondary winding 32 and voltage drop across the spark discharge device 40. The OFF time (T) may then be expressed by the following equation:

where:

L Inductance of the secondary winding 32 R, Resistance of the secondary winding 32 Ln Natural log 1 Initial current in the secondary winding 32 when the energy in the transformer 31 begins to discharge through the spark gap device 40 Since these parameters are fixed for a particular transformer and a particular spark plug, the turnoff time will be constant. Similarly the ON time may be expressed by the following equation:

where:

L, Inductance of primary I, Peak input current E Battery voltage OPERATION When switch 5 is closed the battery 3 applies electrical power to the circuitry allowing a current to flow through primary winding 31, diode 23 and resistor 21 to charge capacitor 9. Simultaneously current flows from the base of transistor 10 through resistors 15 and 16 to ground 1. This turns transistor 10 ON which permits a collector current to flow to ground through resistor 12 and through lead 21 to provide a base current to transistor 20, thereby turning transistor 20 ON. When transistor 20 is ON, current from the battery 3 flows through the primary winding 31 of transformer 30 and through the collector and emitter of transistor 20. With transistor 20 ON a linearly rising current begins to flow through the primary winding 31 of the transformer 30. Due to the inductance of the primary winding this current develops a constant voltage (approximately equal to the input voltage) across the primary winding 31 of the transformer 30. This voltage across the primary 31 causes diode 25 to conduct ON and allow the base current of transistor 10 to increase, thereby increasing the base drive to transistor 20, driving transistor 20 into saturation. Linearly rising inductive current (Icl) continues to flow in the primary winding 31 and until it reaches a peak value equal to 31,, of transistor 20, at which time transistor 20 comes out of saturation. At this time the voltage across the primary winding 31 will drop to zero as the voltage across the transistor 20 increases. This drop in the voltage across the primary starts a regenerative action which drives transistor 20 into the cutoff region. As the primary current decreases, the voltage on the secondary winding 32 reverses. The high voltage produced by the secondary ionizes the spark plug 40 and the energy stored in the transformer 30 is delivered into the plug.

As the voltage across the transistor 20 increases, it charges up the'capacitor 9 through resistor 21. Once capacitor 9 is charged, transistor 14 is turned ON, removing the forward bias from transistor 10 and turning transistor 10 OFF. This removes the current flowing in lead 21 to the base of transistor 20, turning transistor 20 OFF. Transistor 10 stays OFF as long as the voltage across the transistor 20 is high. During the OFF time the voltage across the transistor 20 is approximately equal to the voltage across the spark gap divided by the turns ratio of the transformer 30 plus the voltage of the battery 3. Turning transistor 20 OFF results in a sudden decrease of the current flowing through the primary winding 31 and collector of transistor 20. During this time the rate of change of current (di/dt) becomes sharply negative, the high voltage induced in the secondary winding 32 of the transformer 30 also reverses, and the secondary winding 32 becomes a current source. The high voltage produced by the secondary winding causes an electrical discharge across the spark gap device 40 and the energy stored in the transformer 30 is dissipated in the electrical discharge in the spark gap discharge device 40.

When the energy stored in the transformer 30 is delivered to the spark discharge device 40, the current in the secondary winding 32 goes to zero. Simultaneously, transistor 14 turns OFF and a current starts to flow through resistor 11, emitter-base junction of transistor 10, resistor 12 and lead 21, turning transistor 20 ON. The circuit is now in a state to repeat the above described cycle.

6 In one satisfactorily operable system the ignition a first transistor having collector and emitter tersystem described in FIG. 2 had the values or were of minals connected in series with the primary the types indicated below: winding of said transformer, said first transistor Battery 341 5 volts d-c having alternate conductive and nonconductive Capacitor 9-0.033 microfarads, 25 volts 5 intervals to periodically interrupt the current Diodes 13, 23, 251N645 flowing from the primary winding of said trans- Resistor 11-15 ohms, 1 watt former; Resistor 12l00 ohms, 0.5 watt a second transistor having alternate conductive Resistor IS 1800 ohms, 0.5 watt and nonconductive intervals to control the con- Resistor 16-10K ohms, 0.5 watt 0 duction of said first transistor, said transistor in Resistor 214.7K ohms, 0.5 watt electrical circuit relationship with the base of Resistor 22-lOK ohms, 0.5 watt said first transistor so that when said second Transistor 20 (NPN)2N3772 transistor conducts, a current is supplied from Transistor (PNP)-MJE 371 one of the electrodes of said second transistor to Transistor 14-2N3569 15 the base of said first transistor whereby when Transformer 30Primary 200 turns, No. 18 Seconsaid second transistor conducts, said first dary 21,600 turns, No. 40 Bendix Part No. transistor conducts; and lO-37256l-C1 a zener diode connected in electrical circuit rela- Switch 5-Single pole 2-contact tionship to the base and one other electrode of Zener diode 7-5 volt zener 20 said second transistor, said zener diode having a A prototype unit was built and tested using the aforereverse breakdown potential that prevents variamentioned components and the following results were tions in the magnitude of the voltage of said d-c obtained that clearly demonstrate the current regulaenergy source from affecting the magnitude of tion at the input to the oscillator over a wide range of the collector current of said second transistor input voltages. when said second transistor is conducting whereby a constant current is supplied to the Energy base of said first transistor when said second $83; 3.1%- 322" 8:32? 2:1,, 335;; r e? 1S q p (CPS) i) (kv) 2. The ignition circuit as recited in claim 1 wherein 4 94 212 22 said oscillator means includes: 6 1.92 100 3.54 35.4 22. 8 L85 H4 456 22 a switching circuit for changing sald first and second I0 I 7 132 6-26 4 -6 22 transistors from the conductive to the nonconduc- {g kg :2; g; 25:2 tive state, said switching circuit including: 15 1.45 I58 8.5 53.3 22 a third transistor in electrical circuit relationship with the base of said second transistor for reduc- While a preferred embodiment of the invention has ing the base current of said second transistor to been disclosed, it will be apparent to those skilled in the a value that causes said second transistor to be art that changes may be made to the invention as set nonconductive in response to a current flowing forth in the appended claims, and in some cases certain through said first transistor whereby said third features of the invention may be used to advantage 4O transistor operates with said first and second without corresponding use of other features. For examtransistors to cause an oscillating current to flow ple, different types of semiconductors or solid state through the primary winding of said transcontrol devices may be substituted for the types illusformer.

trated. Accordingly, it is intended that the illustrative 3. In combination with the ignition system recited in and descriptive materials herein be used to illustrate claim 1 wherein said switching network further comthe principles of the invention and not to limit the prises: scope thereof. a capacitor connected between the base of said third Having described the invention, what is claimed is: transistor and the emitter of said first transistor;

1. In combination with a gas turbine engine of the a first and second series connected resistor contype having a spark gap for igniting fuel in the engine nected between the base of said third transistor and an ignition circuit for producing an electrical and the collector of said first transistor; discharge at the spark gap, the improvement wherein a first diode connected across one of said first and the ignition circuit comprises: second resistors to permit the passage of current to a source of d-c energy; said base of said third transistor;

a transformer having a primary and a secondary a third and fourth series connected resistor conwinding, said secondary winding connected across nected between the emitter of said third transistor said spark gap device; and the emitter of said first transistor; and

switching means connected between said d-c energy a second diode connected between the junction of source and the primary winding of said transsaid third and fourth resistors and the collector of former for connecting and disconnecting said d-c said first transistor. energy source to and from said transformer; and 4. The ignition system recited in claim 1 including a transistorized oscillator means connected between fifth resistor connected to the emitter electrode of said said direct current source and the primary winding second transistor and a sixth resistor connected to the of said transformer for periodically interrupting collector electrode of said second transistor, said current flow from said source through said primary second transistor and said fifth and sixth resistors conwinding, said transistorized switching oscillator innected across said primary winding of said transformer cluding: and said first transistor.

fifth resistor connected to the emitter electrode of said second transistor and a sixth resistor connected to the collector electrode of said second transistor, said second transistor and said fifth and sixth resistors connected across said primary winding of said transformer and said first transistor. 

1. In combination with a gas turbine engine of the type having a spark gap for igniting fuel in the engine and an ignition circuit for producing an electrical discharge at the spark gap, the improvement wherein the ignition circuit comprises: a source of d-c energy; a transformer having a primary and a secondary winding, said secondary winding connected across said spark gap device; switching means connected between said d-c energy source and the primary winding of said transformer for connecting and disconnecting said d-c energy source to and from said transformer; and transistorized oscillator means connected between said direct current source and the primary winding of said transformer for periodically interrupting current flow from said source through said primary winding, said transistorized switching oscillator including: a first transistor having collector and emitter terminals connected in series with the primary winding of said transformer, said first transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from the primary winding of said transformer; a second transistor having alternate conductive and nonconductive intervals to control the conduction of said first transistor, said transistor in electrical circuit relationship with the base of said first transistor so that when said second transistor conducts, a current is supplied from one of the electrodes of said second transistor to the base of said first transistor whereby when said second transistor conducts, said first transistor conducts; and a zener diode connected in electrical circuit relationship to the base and one other electrode of said second transistor, said zener diode having a reverse breakdown potential that prevents variations in the magnitude of the voltage of said dc energy source from affecting the magnitude of the collector current of said second transistor when said second transistor is conducting whereby a constant current is supplied to the base of said first transistor when said second transistor is conducting.
 2. The ignition circuit as recited in claim 1 wherein said oscillator means includes: a switching circuit for changing said first and second transistors from the conductive to the nonconductive state, said switching circuit including: a third transistor in electrical circuit relationship with the base of said second transistor for reducing the base current of said second transistor to a value that causes said second transistor to be nonconductive in response to a current flowing through said first transistor whereby said third transistor operates with said first and second transistors to cause an oscillating current to flow through the primary winding of said transformer.
 3. In combination with the ignition system recited in claim 1 wherein said switching network further comprises: a capacitor connected between the base of said third transistor and the emitter of said first transistor; a first and second series connected resistor connected between the base of said third transistor and the collector of said first transistor; a first diode connected across one of said first and second resistors to permit the passage of current to said base of said third transistor; a third and fourth series connected resistor connected between the emitter of said third transistor and the emitter of said first transistor; and a second diode connected between the junction of said third and fourth resistors and the collector of said first transistor.
 4. The ignition system recited in claim 1 inCluding a fifth resistor connected to the emitter electrode of said second transistor and a sixth resistor connected to the collector electrode of said second transistor, said second transistor and said fifth and sixth resistors connected across said primary winding of said transformer and said first transistor.
 5. The ignition system recited in claim 2 including a fifth resistor connected to the emitter electrode of said second transistor and a sixth resistor connected to the collector electrode of said second transistor, said second transistor and said fifth and sixth resistors connected across said primary winding of said transformer and said first transistor.
 6. The ignition system recited in claim 3 including a fifth resistor connected to the emitter electrode of said second transistor and a sixth resistor connected to the collector electrode of said second transistor, said second transistor and said fifth and sixth resistors connected across said primary winding of said transformer and said first transistor. 